From: Yang Weijiang Enable guest shadow stack pointer(SSP) access interface with new uAPIs. CET guest SSP is HW register which has corresponding VMCS field to save and restore guest values when VM-{Exit,Entry} happens. KVM handles SSP as a fake/synthetic MSR for userspace access. Use a translation helper to set up mapping for SSP synthetic index and KVM-internal MSR index so that userspace doesn't need to take care of KVM's management for synthetic MSRs and avoid conflicts. Suggested-by: Sean Christopherson Signed-off-by: Yang Weijiang Tested-by: Mathias Krause Tested-by: John Allen Tested-by: Rick Edgecombe Signed-off-by: Chao Gao Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson --- Documentation/virt/kvm/api.rst | 8 ++++++++ arch/x86/include/uapi/asm/kvm.h | 3 +++ arch/x86/kvm/x86.c | 23 +++++++++++++++++++++-- arch/x86/kvm/x86.h | 10 ++++++++++ 4 files changed, 42 insertions(+), 2 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index abd02675a24d..6ae24c5ca559 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -2911,6 +2911,14 @@ such as set vcpu counter or reset vcpu, and they have the following id bit patte x86 MSR registers have the following id bit patterns:: 0x2030 0002 +Following are the KVM-defined registers for x86: + +======================= ========= ============================================= + Encoding Register Description +======================= ========= ============================================= + 0x2030 0003 0000 0000 SSP Shadow Stack Pointer +======================= ========= ============================================= + 4.69 KVM_GET_ONE_REG -------------------- diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h index 508b713ca52e..8cc79eca34b2 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -437,6 +437,9 @@ struct kvm_xcrs { #define KVM_X86_REG_KVM(index) \ KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_KVM, index) +/* KVM-defined registers starting from 0 */ +#define KVM_REG_GUEST_SSP 0 + #define KVM_SYNC_X86_REGS (1UL << 0) #define KVM_SYNC_X86_SREGS (1UL << 1) #define KVM_SYNC_X86_EVENTS (1UL << 2) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2c9908bc8b32..460ceae11495 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6017,7 +6017,15 @@ struct kvm_x86_reg_id { static int kvm_translate_kvm_reg(struct kvm_x86_reg_id *reg) { - return -EINVAL; + switch (reg->index) { + case KVM_REG_GUEST_SSP: + reg->type = KVM_X86_REG_TYPE_MSR; + reg->index = MSR_KVM_INTERNAL_GUEST_SSP; + break; + default: + return -EINVAL; + } + return 0; } static int kvm_get_one_msr(struct kvm_vcpu *vcpu, u32 msr, u64 __user *user_val) @@ -6097,11 +6105,22 @@ static int kvm_get_set_one_reg(struct kvm_vcpu *vcpu, unsigned int ioctl, static int kvm_get_reg_list(struct kvm_vcpu *vcpu, struct kvm_reg_list __user *user_list) { - u64 nr_regs = 0; + u64 nr_regs = guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) ? 1 : 0; + u64 user_nr_regs; + + if (get_user(user_nr_regs, &user_list->n)) + return -EFAULT; if (put_user(nr_regs, &user_list->n)) return -EFAULT; + if (user_nr_regs < nr_regs) + return -E2BIG; + + if (nr_regs && + put_user(KVM_X86_REG_KVM(KVM_REG_GUEST_SSP), &user_list->reg[0])) + return -EFAULT; + return 0; } diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index 786e36fcd0fb..a7c9c72fca93 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -101,6 +101,16 @@ do { \ #define KVM_SVM_DEFAULT_PLE_WINDOW_MAX USHRT_MAX #define KVM_SVM_DEFAULT_PLE_WINDOW 3000 +/* + * KVM's internal, non-ABI indices for synthetic MSRs. The values themselves + * are arbitrary and have no meaning, the only requirement is that they don't + * conflict with "real" MSRs that KVM supports. Use values at the upper end + * of KVM's reserved paravirtual MSR range to minimize churn, i.e. these values + * will be usable until KVM exhausts its supply of paravirtual MSR indices. + */ + +#define MSR_KVM_INTERNAL_GUEST_SSP 0x4b564dff + static inline unsigned int __grow_ple_window(unsigned int val, unsigned int base, unsigned int modifier, unsigned int max) { -- 2.51.0.384.g4c02a37b29-goog